You must have static IPs set up, and both computers are trying to connect with the same IP, which cannot be done. You'll have to edit the network settings for the connection and change the IP for one of the computers (just increase the value of the number on the end by 1 or something). Alternatively you can set up DHCP to automatically give out IP addresses and then you won't have to worry about that. You can find out how to do that in the manual of your router. If you can't find it or have lost it I have included links below to the most common manufacturers. Router manufacturer download pages (for software/drivers/manuals)
- D-Link (North America and UK)
- Netgear (Worldwide and UK)
- Linksys (Worldwide)
- Belkin (USA and UK)
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and victorious in war shall be made glorious in peace.